1. Technical Field
Exemplary embodiments of the invention relate generally to electronic devices such as inverters. Other embodiments relate to safety or failsafe circuits for electronic devices.
2. Discussion of Art
Some vehicles may employ electric traction motors for driving wheels of the vehicles. In some of these vehicles, the motors are alternating current (AC) motors whose speed and power are controlled by varying the frequency and the voltage of AC electric power supplied to the field windings of the motors. The electric power may be supplied as DC power that is converted to AC power of controlled frequency and voltage amplitude by a circuit such an inverter. The inverter may include semiconductor switches such as insulated gate bipolar transistors (IGBTs) that are switched on and off by drive circuitry in an alternating fashion to produce an output AC waveform.
The IGBT can be conceptually understood as a bipolar transistor driven by a power MOSFET. It may have an advantage of being a minority carrier device (good performance in on-state, even for high voltage devices), and may have the high input impedance of a MOSFET (it can be driven on or off with a very low amount of power). But, in a low voltage application there may be an undesirable high voltage drop exhibited in the on-state (2 to 4 V). Compared to a MOSFET, the operating frequency of an IGBT is relatively low. This may be because of a so-called ‘current-tail’ problem during turn-off. This problem may be caused by the slow decay of the conduction current during turn-off. The net result may be that the turn-off switching loss of an IGBT is relatively higher than its turn-on loss. Turn-off energy multiplied by the switching frequency of the intended application may allow for an estimate of the turn-off loss.
It may be desirable to have an electronic device or circuit, such as an inverter, that differs from those devices or circuits that are currently available.